EPSP (5-enolpyruvylshikimate-3-phosphate) synthase is an enzyme that catalyzes the conversion of phosphoenolpyruvate and 3-phosphoshikimate to phosphate and 5-enolpyruvylshikimate-3-phosphate (EPSP), and it participates in the biosynthesis of the aromatic amino acids phenylalanine, tyrosine, and tryptophan. Glyphosate, the top selling herbicide in the world, acts a competitive inhibitor for phosphoenolpyruvate.
Glyphosate tolerant crops have been created by introducing glyphosate-insensitive 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) enzymes into plants. In one example, maize event NK603 uses EPSPS from Agrobacterium sp. strain CP4. The enzyme is highly insensitive to inhibition by glyphosate while retaining catalytic efficiency similar to native plant enzymes (Sikorski and Gruys. 1997. Acc. Chem. Res. 30:2-8). In another example, maize event GA21 uses a double mutant maize EPSPS in which threonine at position 103 is changed to isoleucine and proline at position 107 is changed to serine.
Plant EPSP synthases having kinetic properties that provide adequate tolerance to glyphosate and catalytic capacity to sustain normal rates of metabolic flux are desired.